The present invention relates to an air conditioning system for vehicles and, more particularly, to a system for controlling a capacity of a compressor in response to a mist on a vehicle windowpane.
In general, a vehicle has installed therein an air conditioning system by which comfortable, conditioned air is blown into a compartment.
Japanese Provisional Utility Model Publication (Kokai) No. 59-92013 discloses an air conditioning system as shown in FIG. 1. The system comprises a duct 1 having at its upstream end an air intake section 2 and at its downstream end an air blowoff section 3 which communicates with a vehicle compartment. The air intake section 2 is comprised of an indoor-air inlet 2A and an outdoor-air inlet 2B. An indoor-air/outdoor-air selecting damper 2C is provided for selectively opening one of the inlets 2A and 2B. The air blowoff section 3 is comprised of a vent blowoff outlet 3A directed toward the face of an occupant, a defrost blowoff outlet 3B, and a heat blowoff outlet 3C directed toward the feet of the occupant. Mode selecting dampers 3D and 3E are provided for selectively opening and closing the blowoff outlets 3A, 3B and 3C.
A blower 4 variable in amount of blown air is disposed in the upstream end of the duct 1. The blower 4 is adapted to draw air into the duct 1 through the air intake section 2, cause the air to flow through the duct 1 and, subsequently, cause the air to be blown into the compartment through the air blowoff section 3. The blower 4 is driven by drive means 4A.
A refrigerating cycle 5 comprises an evaporator 6 arranged within the duct 1, a condenser 7, and a compressor 8. By the refrigerating cycle 5, the air passing through the duct 1 is cooled.
A heater core 9 is arranged in the duct 1 downstream of the evaporator 6, for heating the air passing through the duct 1.
An air-mix damper 10 located upstream of the heater core 9 is angularly movable about a pivot 10'so that an amount of air passing through the heater core 9 varies depending upon the angular position of the air-mix damper 10. Thus, the temperature of the air flow is determined depending upon the angular position of the air-mix damper 10. The air-mix damper 10 is actuated by actuator means 10A between a full-cool position indicated by the solid line and a full-heat position indicated by the dot-and-dash line.
Various sensors are provided which include an indoor-air temperature sensor 11 for detecting a temperature Tr within the compartment, an outdoor-air temperature sensor 12 for detecting a temperature Ta of the oputdoor air, and an insolation sensor 13 for detecting an amount of insolation Ts. Outputs from the respective sensors 11, 12 and 13 are sent to control means 15 to be described later. A temperature setter 14 provided into which it is possible to input a temperature desired to be set as a temperature within the compartment, i.e., a desired set temperature TD.
The control means 15 includes a synthetic signal arithmetic unit 16 and a control unit 17. Based on the indoor-air temperature TR, the outdoor-air temperature TA, the amount of insolation TS and the set temperature TD, the synthetic signal arithmetic unit 16 determines a synthetic signal T in accordance with the following equation: EQU T=aTr+bTa+cTs-dTD (1)
where a, b, c and d are constants.
The control unit 17 comprises blower control means 18 for controlling the blower 4 on the basis of the synthetic signal T, damper control means 19 for controlling the indoor-air/outdoor-air selecting damper 2c on the basis of the synthetic signal T, damper control means 20 for controlling the air-mix damper 10 on the basis of the synthetic signal T, mode control means 21 for controlling the mode selecting dampers 3D and 3E, and compressor control means 22 for controlling the compressor 8 on the basis of the synthetic signal T.
When a dew condensation sensor, not shown, detects a mist on a vehicle windowpane, demist control is carried out. The demist control does mean control in which the indoor-air inlet 2A is opened and the compressor 8 is driven to actuate the refrigerating cycle 5, and the defrost blowoff outlet 3B is opened to blow dried air against the windowpane, to thereby clear off the mist on the windowpane. Such demist control may be carried out by the driver's operation of a demist switch.
The assignee of the present application has disclosed a so-called variable capacity type compressor as such compressor 8, in Japanese Provisional Utility Model Publications (Kokai) Nos. 59-92013 and 59-76410, both assigned to the assignee of the present applications. The compressor has a capacity varying mechanism which is controlled by a capacity setter.
When such a condition is satisfied that a mist occurs on an inner surface of a windowpane, if the compressor has already been turned on and been run, the capacity of the compressor is increased by a predetermined amount to increase the dehumidification performance of the compressor, making it possible to quickly clear off the mist.
However, the air conditioning system constructed as described above has various problems which will be discussed below.
When a mist on the windowpane is detected, the capacity of the compressor is increased step by step. Therefore, it takes considerably long time to remove the mist. In addition, there may be a case where the capacity of the compressor required for the air conditioning control increases with an increase in the outdoor-air temperature. Under such circumstance, there may be a case where the compressor capacity required for the air conditioning control becomes greater than the compressor capacity required for the demist control. In such case, however, even if the compressor capacity required for the air conditioning control is greater than that required for the demist control, the compressor capacity is brought to the capacity required for the demist control. This is not preferable for the air conditioning control.
Moreover, so long as the mist on the windowpane is not cleared off, the compressor capacity continues to increase. Accordingly, even if the vehicle compartment is very low in temperature, the compressor would be run under the maximum capacity. This would result in remarkable sacrifice of the temperature control within the compartment.